Conventionally a butterfly valve has been known as a device to open and close a fluid flow path to control a flow rate (see, for example, Japanese Unexamined Patent Application Publication No. 2004-293452 and Japanese Unexamined Patent Application Publication No. 2010-106738). The butterfly valve controls the flow rate of the fluid through the orientation of a valve unit by opening and closing a flow path through rotating the valve unit, which is shaped as a disk that is provided in the flow path, around an axis that is perpendicular to the flow path.
Conventionally, as a flow rate controlling device there has been a throttle device for an internal combustion engine as set forth in Japanese Unexamined Patent Application Publication No. 2004-293452, below.
FIG. 56 is a lateral sectional view of the vicinity of a conventional throttle valve of a throttle device for an internal combustion engine as set forth in Japanese Unexamined Patent Application Publication No. 2004-293452.
In the throttle device for the internal combustion engine in Japanese Unexamined Patent Application Publication No. 2004-293452, a throttle valve 201 that is secured on a throttle shaft 202 is attached so as to be able to rotate within an air intake path that is formed within a bore inner tube 252 that has a circular cross-sectional shape, in a throttle body 205. A boss-shaped protruding portion 256 is provided in a center portion of the air intake path, where a fully closed stopper 207 and a fully opened stopper 208 are formed integrally at the two end surfaces of the boss-shaped protruding portion 256.
The air intake path is placed in the fully opened state by rotating the throttle valve 201 to contact the fully opened stopper 208 (referencing reference symbol 201 of the solid line in FIG. 56). On the other hand, the air intake path is placed in the fully closed state by rotating the throttle valve 201 to contact the fully closed stopper 207 (referencing reference symbol 201 of the dotted line in FIG. 56).